1. Technical Field
The present invention relates to a photosensitive composition, a method for forming pattern, and a method for manufacturing a semiconductor device.
2. Related Art
A lithographic technology is employed as a technology for manufacturing a semiconductor element. A chemically amplified photoresist having a characteristic of higher sensibility is employed in the lithographic technology.
The chemically amplified photoresist contains materials of a binder prepared by introducing a protective group in a base resin, which is soluble to a liquid developer, to reduce the solubility of the resin, and a photosensitive composition composed of a photo-acid generator for generating acid by an irradiation of a high energy ray and the like.
In the lithographic technology employing the chemically amplified photoresist, acid is generated from a photo-acid generator by exposing to light, and protective group causes a deprotection reaction by heating. The binder resin is deprotected to change the solubility to a liquid developer to be soluble. This allows a photoresist being soluble in a liquid developer, achieving a pattern formation.
The increased level of the recent LSI integration accelerates the miniaturization of the electronic circuit, and a formation of pattern features smaller than 50 nm is required. This causes a reduced wave length of light utilized for exposure from 248 nm of krypton fluoride (KrF) excimer laser, through 193 nm of argon fluoride (ArF) excimer laser, to 13.5 nm of extreme ultraviolet (EUV). The wave length 13.5 nm of such light source is shorter by one tenth or smaller than the wave length of the ArF excimer laser, which is currently employed for a light source in the commercial production, and thus higher resolution is expected.
A use of a photosensitive composition, namely a photoresist, is also required as a material for creating patterns in the EUV lithography, and a use of a chemically amplified photoresist is considered due to its higher sensitivity.
In order to achieve a production of a semiconductor element with higher performance, a higher resolution in lithography and reduced surface roughness on the side wall of the photoresist pattern are required. For example, large roughness on the side wall of the pattern causes an irregularity on the side wall (so-called “line edge roughness”) from an upper viewpoint. Such line edge roughness is transferred during an etching process for a workpiece to deteriorate a dimensional controllability, and reduces the production yield. Therefore, a lithographic technology with improved resolution and reduced line edge roughness is requested.
Currently, various types of lithographic technologies employing high energy beam as statement above are proposed (for example, Japanese Patent Laid-Open No. 2004-062,044, Japanese Patent Laid-Open No. 2004-219,813, Japanese Patent Laid-Open No. 2005-213,215, Japanese Patent Laid-Open No. 2008-107,817, Japanese Patent National Publication No. 2004-530,921, and Japanese Patent National Publication No. 2005-508,512).
However, the conventional technologies described in the above-described patent publications contains the following problems to be improved.
First of all, there is a room for improvement in view of the resolution. For example, when a photoresist is exposed to a high energy beam such as an EUV radiation, energy of a photon is larger than the ionization energy for the photoresist material. Therefore, atom composing the photoresist material is brought into highly excited state with the EUV radiation to be ionized. Since the photoelectron generated by such ionization process is in higher energy state, the photoelectron travels from the location where the EUV radiation is absorbed and scatters through the photoresist, and then is reached to a thermal equilibration, and after that, is reacted with a photo-acid generator to generate an acid. The distance for travelling electron is considered as about 5 nm. In other words, additional travelling of about several nanometer is required for attaining a thermal equilibrium for photoelectron, as compared with the conventional lithography, so that the resolution for the photoresist is reduced, causing a problem of increased roughness on the side wall of the photoresist pattern.
Secondly, there is a room for improvement in view of sensibility. Since the energy of photon in the EUV radiation is larger, less photons incident to the photoresist are required to achieve an exposure with the same sensibility as employed for the conventional photoresist. Thus, problems in deficient sensibility is caused, in which the amount of light for the exposure is not sufficient for inducing the reaction similarly as in the case of employing the conventional photoresist.
Improvements in the resolution and the sensibility are common targets in not only the EUV lithography but also the lithography employing high energy beam.